The °Brix content of the finished tomato product is largely controlled by the processor and manufacturing process.
Managing tomato taste
Flavor is generally related to the relative concentrations of sugars and acids in the fruit, mainly fructose and citric acid. The best, most flavorsome combination is a high sugar and high acid content.
A normal pH range in tomatoes is 4.0- 4.5 and the lower the pH, the more tart or sour the fruit. Flavor is normally measured by taste panels who rate the tomato for a range of characteristics including smell, aroma, firmness, juice, mealiness, skin texture, acids and sugars.
Some countries have established quantifiable indicators of a fruit’s flavor. For example, in France, flavor is assessed by examining the balance of sugar and total titratable acid. The French prefer a sugar:acid ratio of 10 and an acid content of 5g of hydrated citric acid/l.
Volatile compounds also contribute to flavor, and more than 130 of these compounds have been identified. There is a direct relationship between the color and flavor because some volatile compounds are derived from oxidation of carotenoids.
Sugar levels in tomato
°Brix is a measure of the Total Soluble Solid (TSS) content in the tomato or tomato product. The TSS in tomatoes is mainly sugars (fructose). A tomato juice, which is assessed as having 20 ° Brix, has 200g/litre of soluble sugars.
Tomatoes for processing require a minimum °Brix of 4.5. This compares with an acceptable range of 3.5 - 5.5 in fresh tomatoes. The TSS of processed products is measured by refractometry.
However, some processors do pay a higher price for higher dry matter tomatoes. In general, smaller, cherry tomatoes have a higher brix ratio and are sweeter than larger round or common tomatoes.
Crop Nutrition and Tomato Taste
Nitrogen
High rates of nitrate applied as calcium nitrate increase levels of total soluble solids as measured by °Brix.
Phosphorus
Potassium also increases TSS within the tomato. As well as improving processed tomato product quality, this has benefits in terms of improved taste and storage of fresh tomatoes.
Sulfur
Sulfur increases fruit TSS.
Copper
Application of Copper in deficient soils improves fruit quality
Acidity levels in tomato
Measurement of acidity is by simple pH assessment with a range of pH 4-5 being typical for tomato. Total acidity, can be measured by chromatography or enzymatic reaction – where 0.35 – 0.40g/100cc juice is required. Alternatively, processors measure total titratable acidity or volatile acidity after distillation.
Within the EU, tomato juice and concentrates require titratable acidity of <10% citric acid; juice and soup need a pH of 4.5 - 4.6 for proper sterilization. Often, though, some form of citric acid or lemon juice is added prior to canning.
Potassium
Higher levels of potassium in the plant, increases the acidity of the fruit and the resultant tomato juice.
